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Ventilation to eliminate oxygen deficiency in a confined space. Part I: a cubicle model.

Effectiveness of ventilation for restoration of deficient oxygen levels was investigated in a confined space (CS) model. The study addressed certain essential parameters in the design of ventilation for a CS including: space configuration, means of ventilation, ventilation flow rate, and ventilation inlet/outlet elevation in the CS. A cubicle model was used which measured 0.61 meters on each edge. The removable top had an opening for insertion of a ventilation pipe the diameter of which was 25 percent of the edge length. Nitrogen was introduced from a pressure cylinder through the bottom of the CS model to create the oxygen deficiency in the atmosphere. Samples of air were taken from inside the CS at four specific locations. Oxygen recovery was first tested in open top and closed top cases without mechanical ventilation. Without mechanical ventilation, the open top case recovered in less than 2 minutes, while the closed top case took 70 to 80 minutes to recover. In one of the ventilation studies, tracer smoke was generated in a continuing stream which was introduced into the CS in a controlled method at several locations. Results indicated that oxygen recovery was more rapid for supply ventilation than for exhaust in the CS. Efficiency was also affected by inlet/outlet elevation and location in the CS in which alignment provided the most rapid ventilation, and distant location was delayed. Decreasing flow rate positively affected efficiency of ventilation to a cut off point after which little improvement was noted. The authors conclude that mechanical ventilation can work efficiently in correcting oxygen deficiency in confined spaces.